Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-11-02
2001-06-05
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S089000, C347S091000, C347S056000
Reexamination Certificate
active
06241344
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus which jets ink to adhere on a recording medium and to form an image.
2. Description of the Related Art
Heretofore, various non-impact recording type image forming apparatuses including electrophotographic systems have been developed. Among these non-impact recording systems, on-demand type ink jet recording systems, which are advantageous in price reduction, reduction of running cost, minimization of the apparatus, and low noise level, have drawn attention, and various types of ink jet recording apparatuses have been developed and commercialized.
A typical on-demand type ink jet recording apparatus is provided with a passage for supplying ink, a nozzle or an aperture for jetting ink, and a mechanism for generating a pressure to jet ink. In particular, the thermal type which uses a heat generating element and the piezoelectric type which uses a piezoelectric element as a mechanism for generating the pressure have been known as the typical on-demand types. In the thermal type, ink droplets are jetted from the nozzle head with a vapor pressure generated by heat generated from a heater provided in an ink passage and adheres on a recording medium, and an image is formed. For example, Japanese Published Unexamined Patent Application No. Sho 54-51837 and Japanese Published Unexamined Patent Application No. Sho 54-59139 disclose such an on-demand thermal type ink jet recording apparatus. In the piezoelectric type, the volume of a passage is changed by displacement of a piezoelectric element provided in the passage, ink is jetted from the nozzle head by the pressure and adheres on a recording medium, and an image is formed. For example, Japanese Published Unexamined Patent Application No. Sho 53-12138 and Japanese Published Examined Patent Application No. Sho 53-45698 disclose such an on-demand piezoelectric type ink jet recording apparatus.
In the conventional ink jet system in which ink droplets are jetted from a nozzle or an aperture, ink having low viscosity in a range from 1 mPa·s to 3 mPa·s is used, and ink is jetted from a nozzle or an aperture having a small diameter in a range from 30 &mgr;m to 50 &mgr;m. Because the viscosity of ink is low, the reduction of the ink quantity in the nozzle or aperture due to ink jetting is re-filled at high speed from an ink storage unit. Therefore, because the meniscus (interface between ink and air) in the nozzle head or aperture resumes rapidly, ink jetting is stable even though high speed printing at a repeating jetting frequency exceeding 10 kHz is performed.
However, in the case that low viscosity ink is printed on a normal paper, fast ink penetration causes feathering along fibers of the paper, the feathered image feels rough and results in reduced image quality. When adjacent dots are concatenated due to feathering, the resolution is reduced on that portion, and the image quality is deteriorated severely. Suppression of penetration speed by controlling the surface tension of ink causes inter color bleeding with ink of different color which is jetted on the adjacent spot, also resulting in deteriorated image quality severely.
To solve the above-mentioned problem caused from low viscosity ink, the use of high viscosity ink helps the penetration speed of the ink into a recording medium to be slowed and prevents feathering, and also helps the bleeding speed between different colors to be slowed and prevents bleeding, and the use of high viscosity ink is very effective for solving the above-mentioned problem.
With the extensive diffusion of recording apparatuses using ink jet system, application is widening rapidly, and therefore the wide variety of recording media have been used. It is desired that the ink jet recording system is applied not only to paper but also to various non-water absorptive media such as metals, plastics, and glasses, and it is desired that the ink jet recording apparatus which is capable of using high viscosity and tacky ink is realized.
However, it is difficult for the conventional ink jet system having a nozzle or an aperture to make use of high viscosity ink because the passage resistance is high and the ink supply speed is very low. With an increase of the passage resistance, the energy required to jet ink increases. For example, if an ink jet apparatus which normally uses commercially available water color ink (having a viscosity in a range from 1 mPa·s to 3 mPa·s) uses high viscosity ink, the ink supply becomes insufficient if the ink viscosity is higher than 10 mPa·s, and the resumption of meniscus cannot follow the ink consumption. Ink jetting in such state results in scattered ink jetting quantity and jetting direction and results in poor picture quality because ink is jetted from the unstable meniscus position. When ink having a viscosity exceeding 20 mPa·s is used, the ink supply delays from consumption severely, and irregular jetting is caused. Further, when ink having a viscosity exceeding 100 mPa·s is used, even if the supply can follow the consumption, the energy generated from the conventional pressure generation unit to jet the ink is insufficient, the ink is jetted unstably or no ink is jetted.
To solve such a problem, for example, Japanese Published Unexamined Patent Application No. Hei 9-169111 proposes a printer in which a nozzle having a large diameter in a range from 50 &mgr;m to 70 &mgr;m is used to reduce the passage resistance, and high speed printing is realized in spite of using high viscosity ink having a viscosity in a range from 10 mPa·s to 100 mPa·s. In this method, the ink supply delays from the ink consumption and repetition printing frequency decreases unless the larger nozzle diameter corresponding to the incremental ink viscosity is used. However, the larger nozzle diameter results in a relatively increased diameter of jetted ink droplets and results in reduced resolution and poor image quality.
To solve the above-mentioned problem, for example, Japanese Published Unexamined Patent Application No. Sho 62-90257 proposes a method in which solid ink is heated so that the viscosity is reduced to a low viscosity in a range from 5 mPa·s to 10 mPa·s, and the ink is jetted in the same manner as used in a normal ink jet system, the ink is cooled and solidified immediately when the ink adheres on a recording medium, and recording is performed. However, in this method, the head unit should be heated always, such heating results in increased energy consumption. Further, because ink droplets are solidified at the moment when the ink droplets adhere on a recording medium, the ink scarcely penetrates into the recording medium, and such insufficient penetration causes a fixing problem. In addition, ink droplets are solidified in the form of a semisphere, and such a semisphere results in the rough surface of the image. The light is scattered on the image surface, the glossiness of the image is reduced, and the color turbidity of OHP is caused, and therefore this method involves many problems.
Further, for example, Japanese Published Unexamined Patent Application No. Sho 56-4467 proposes a method in which ink is jetted from a nozzle or a slit aperture by attracting the ink electrostatically. This method is advantageous in that the ink supply is significantly independent of ink viscosity because the ink is jetted and supplied simultaneously and the ink droplet diameter is not very dependent on the nozzle diameter or the slit width. However, the high viscosity causes long stringing when the ink is attracted, and it is difficult to form fine dots. Further, satellite drops are generated from the stringing portion, and the image quality becomes very poor. If ink having higher viscosity is used, the cohesion of the ink is larger than the electrostatic attractive force, the printing becomes impossible.
Some ink jet systems having no nozzle have been proposed though they are not commercialized. For example, Japanese Published Unexamined Patent Application No. Sho 51-132036 proposes a method in which m
Barlow John
Fuji 'Xerox Co., Ltd.
Mouttet Blaise L
Oliff & Berridg,e PLC
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